Sulfur-containing coals, when combusted, produce flue gases which contain sulfur oxides. Because environmental considerations dictate strict limitations on the amount of sulfur oxides which may be released to the atmosphere, considerable attention has been devoted by prior art workers to reducing the sulfur oxide levels in flue gases. Unless sulfur oxide levels in flue gases are reduced to acceptable levels, the flue gases produced by many types of coal cannot be released to the atmosphere. The prior art has generally focussed on reducing sulfur content in flue gases by reducing sulfur oxides either to elemental sulfur or to hydrogen sulfide.